The goal of glaucoma therapy is to achieve long-term mean intraocular pressure (IOP) reduction. IOP is a dynamic variable and exhibits significant unpredictable fluctuation. This fluctuation complicates the assessment of glaucoma treatment efficacy: following the initiation of therapy, an observed change in IOP may be attributable to therapeutic change, spontaneous change, or a combination of both. The ideal approach would be to attain numerous pre-treatment IOP measurements and numerous on treatment IOP measurements, in order to establish the mean IOP reduction attributable to therapy. Unfortunately, IOP cannot be easily self-measured; generally, the only measurements available are those obtained in the physician's office during visits that are typically scheduled at intervals of three or four months. Therefore, characterizing short-and long-term IOP behavior, and the change in IOP after initiation of lOP-lowering therapy, using such a low sampling rate is difficult if not impossible. The monocular therapeutic drug trial was developed to provide clinicians with a means of predicting long-term therapeutic IOP reductions using limited short-term data. The monocular trial depends on the validity of several assumptions, including symmetry of IOP variability between fellow eyes, symmetry of IOP responses to therapy between fellow eyes, and the lack of a contralateral crossover effect from unilateral therapy. Each of these assumptions has been challenged by recent data, and numerous recent studies of the monocular drug trial demonstrated that it poorly predicted the fellow eye's response to therapy. An effective alternative to the monocular trial is needed to permit short-term determination of long-term treatment efficacy. We have developed several candidate methods for short-term determination of the long-term efficacy of lOP-lowering therapy. Our hypothesis is that one or more of these will better predict long-term IOP reduction than the monocular drug trial. Our specific aims are (1) to demonstrate that the monocular trial, the current clinical standard, inadequately predicts long-term IOP reduction; and (2) to determine if any of the candidate short-term assessment models adequately predict long-term IOP reduction. To accomplish these aims, we will enroll subjects with glaucoma or ocular hypertension in a clinical trial in which each subject's response to topical medical lOP-lowering therapy will be evaluated using each model. Each model's performance will be compared to the gold standard: mean IOP reduction (the difference in the mean of three pre-treatment and three on-treatment IOP measurements), by determining intraclass correlation coefficients for each model. The results of this study may help eyecare providers make accurate short-term estimates of long-term drug efficacy when starting glaucoma therapy. This will help glaucoma patients achieve adequate reduction of eye pressure more quickly, and avoid long-term use of ineffective medications, all with fewer office visits.